Concentration of coal



Jan. 10, 1928.

w. w, STENNING CONCENTRATION OF COAL grizzlies (bar screens),

Patented Jan. 10, 1928.

UNI' IED' $1ATES-PATENT OFFICE.

WILLIAM WARWICK STENNING, 01 LONDON, ENGLAND, ASSIGNOR TO- MINERALS AMERICAN CORPORATION, OF NEW YORK, N. Y.

BEPARATION NORTH CONCENTRATION OI COAL.

Application fled February 15, 1924, Serial Io. 892,955, and in Great Britain February 16, 1823.

This invention consists of improvements in or relating to the concentration of coal, and particularly relates to improvements applicable directly to the means at present in use for washing coal.

In existing coal washing plants a typical and ordinary method is as follows :The coal as mined is passed over three-inch and the material that passes through is sent to the washery to be cleaned by jigs. The first jig through which the material passes is adjusted so that-the wash water carries as much as possible of the coal, while the coarse shale is eliminated. e finer portions of the recovered coal still contain a considerable amount of finely divided shale. The recovered product is screened into marketable sizes above halfinch. All material below half-inch is reelevated by any suitable appliance and the wash water is re-elevated by a centrifugal pump to a second jig adjusted to deal with this size of materia. The'recovered coal, together with the whole of the wash water, passes to drainage screens, filters, drainage elts, drainage bunkers, or the like: the water from the drainage operation is allowed to settle and is then re-used for washing.

In jigs and equivalent apparatus the principle on which particles of coal are separated from articles of shale is that in water the rate of fall of the coal particles is less than the rate of fall of the shale particles (of comparable size). Concentrators operating on this principle will be referred to hereinas grav1ty concentrators, and in coal washeries the jig is the commonest type.

The existing system above referred to is subject to several important defects. The method is not adapted to the concentration of coal particles of linear dimensions less than of an inch. Fine particles of coal and shale settle very slowly, and the wash water containing these fine particles progressively thickens in re-use, and its specific gravity lncreases, with the result that the action of the jigs, which de ends on the difference between the rate 0 fall of the coal particles and the shale particles respectively in the liquid, is affected detrimentally. Further, a. serious loss of fine coal is incurred. There is often-a difiiculty in the drainage of the coal which is concentrated,

and on the other hand the settlement of shale, gangue, and other suspended matter from the wash waters is exceedingly troublesome.

In coal washing of the type which involves the use of jigs or like gravity concentrators and/or settling tanks in which aqueous liquor or coal-bearing pulp is pumped by a centrifugal pump from one part of the a paratus to another, the advantages of t e presentinvention may be obtained by introducing air into the centrifugal pump, and adding to the aqueous liquor, before or when it enters the pump, a small proportion (say 0.1% or less) of a frothing agent such as cresol, with or without a small proportion (say 0.1% or less) of a froth-stabilizing agent such for example as kerosene oil, anthracene oil or creosote oil. The percentages referred to are measured on the weight of the crude or screened coal to be treated.

his invention also includes in coal washery apparatus the combination with a gravity concentrator, such'as a jig, and a centrifugal pump arranged to deliver aqueous liquor or coal pulp thereto, of means for introducing air, as into the zone of reduced pressure of the pump, and means for introducing a frothing agent and/or oil or like flotation agent as into the liquor or pulp entering the centrifugal pump.

The invention further includes in a coal washery the combination with a washer water reservoir of an outlet for slurry lea ing to an agitator and aerator (conveniently a centrifugal pump having an airinlet to its suction zone), means for introducing frothing agent, as to the slurry before its admission to the agitator, and a chamber communicating with the outlet from the agitator in which the pulp may come to a state of comparative rest so that a coal-bearing froth may rise and be removed.

The results of the treatment according to this invention are, firstly, that the mixture of coal, shale, and water is aerated when it is introduced into the jig (the air bein very finely subdivided owing to the agitation in presence of the frothing agent), and this aeration diminishes the specific gravit of the ulp (i. e. diminishes the density 0 the fluid medium as a whole) and so facilitates the jigging operation, i. e. facilitates the fall of the comparatively large particles of shale but in any case, owing to the flocculated condition of the fine coal, produced by the added reagents and the aeration and agitation, the drainage of the coal is facilitated; and the water which drains away carries only finely divided shale in suspension. The settlement of the shale in the settling tanks is also facilitated.

The accompanying drawing is a diagrammatic representation of a typical coal washing plant to which the present invention has been applied.

The coal is delivered on to a grizzly 10 which allows pieces smaller than 3% in linear dimensions to drop into the well 11 of an elevator 12. The coal delivered by the elevator is carried by the force of a. stream of water, issuing from a pipe 13 into a jig 14. The jig 14 is adjusted to remove shale coarser than one half-inch, which passes to a bin 15. The coarse and fine coal with the fine shale ass to a screen 16. Sizes of coal above one half-inch are graded by the screen and passed to bins diagrammatically shown at 17. Coal and shale below one half-inch pass the screen and are collected with the water from the jig at 18 and passed to a centrifugal pump 19.

The centrifugal pump 19 conducts the material to a second jig 20. This pump 19 is provided with an air inlet 21 on the suction side of the pump and air in quantities suitable for aeration and flotation is introduced, either by the suction or assisted by pressure. At or near the inlet for pul to the centrifugal pump 19 an inlet 22 1s provided for flotation agents, and there is added a frothing agent, such as cresol, at the rate of about 2 lbs. or less per ton of coal, and a froth-stabilizing agent, such as kerosene oil, at the rate of 3 lbs. or less per ton of coal. Where sea-water is used in the washery, the frothing agent may be omitted, or reduced in quantity.

In the second jig 20 the finely divided coal rises to the surface in the form of a froth. There are also some light floccules which are very readily carried upwards in the 'ig, and the separate coal particles not included in the froth are recovered by the normal operation of the jig. The overflow containing the recovered coal passes to the drainage belt 23 and all the coal which has been recovered in the froth, or in floccules, together with larger discrete particles, is retained on the drainage surface. Thus when the treatment in the second jig is thoroughl eflicacious the water carries away only sha e and other,

gangugslime.

I The dr'ainedfine coal passes to a storage bin .24 and the Wat est ttli g nk 25. The overflow rom the settling 25 is re-elevated by a centrifugal pump 26 to the first jig 14, and any make-up water which is re uired may also pass through the pum 26. his pump may be supplied with air 't rough an inlet 27, and, unless the circuit water already contains sufficient, frothing and/or froth-stabilizing reagents may be added at 28. As a result a substantial amount of fine coal is recovered with the coarse coal in the first jigging operation the remainder of the fine coal being recovered by flotation in the second jigging operation.

In coal washeries it is a common practice to employ a large conical or V-shaped tank as a reservoir for circuit water. The tank 25 is shown herein as of such a construction. The water which has been used in the various sta esfiof coal washing is ordinaril run into suc1 a V-tank. The water usually carries slurry with f it. Commonly the V-tank is arranged with an inlet near the top, an outlet for slurry at the bottom and an overflow launder around the upper periphery, into which comparatively pure water overflows on its we back to the washery for further use. T is tank is frequently referred to as the washery water reservoir.

If the water entering the tank 25 contains any fine coal still in suspension, as for example if the treatment in the jig 20 has failed to remove all traces of coal, or if the addition of the air and frothing agents at 21, 22 is omitted, it is desirable that such fine coal shall be removed before the water is returned for re-use in the circuit According to this invention therefore the outlet 29 for slurr from the tank 25 may deliver to a centri ugal pump 30 which has an inlet 31 for air and an inlet 32 for a frothing agent such as cresol, with or without a small proportion of froth-stabilizing agent. 'The aerated and agitated pulp is then led by a pipe 33 into a chamber 34 in which the plup comes to a state of comparative rest. Here a coal-bearing froth may rise to the surface and be removed. The lower art of the chamber 34 is connected by a con uit 35 to the washery water reservoir 25, so that the washery water, substantially depleted of its coal. content, is returned to the reservoir. The chamber 34 in which the froth is formed may be provided at its lower part with an outlet 36 for gangue. Relatively clean water therefore overflows the tank 25 and is returned for reuse.

Hitherto coal particles of linear dimenslons exceeding of an inch have been successfully separated, from impurities by well-known coal-washing apparatus, such the coal ing a frothing as jigsi Finely divided coal particles, articularly those of linear dimensions less t an of an inch have been successfully separated from impurities by froth-flotation, and methods have been sug ested, for example in British atent to ones and Minerals Separation ltd. No. 183,504, for separating associate matter; It will be seen that according to the i'esent invention the concentration of coalparticles of all dimensions dealt with in coal washing (e. from3 inches downwards) is successively accomplished in onescries of operations, and as no special or expensive plant is required in addition to that already commonly in use, the benefits ofthis invention .can be obtained without increased cost, increased labour, or increased power.

I claim:

1. The rocess of separatin coal from coarse and fine broken shaleearing coal which consists in passing the broken shalebearin coal through a bubble containing liquid in the presence of a reagent facilitating the formation of a froth so that coarse coal is separated from the intermixed coarse shale b differential settling in such liquid of the s ale to a level below the coal and fine coal tends to adhere to bubbles and to be lifted thereby out of the shale layer, and separating the coarse and fine coal fromthe liquid.

2. The rocess of separating coal from coarse and fine broken shale-bearing coal which consists in passing the broken shalebearing coal through a liquid containing a flocculating agent tending to flocculate the fine coal so that coarse coal is separated from the intermixed coarse shale by dilferential settling in such liquid of the shale to a level below the coarse coal and fine coal tends to flocculate into shale-free agglomerates and associate itself in such liquid with the coarse .coal, and separating coarse and fine coal substantially together from the liquid carrying the shale. Y

3. The process of separating coal from coarse and fine broken shale-bearing coal, the coarse coal bein too coarse to be floated by bubble action, w ich consists in passing the broken shale-bearin coal through a li uid containing multitu es of bubbles whic lower the density'of the li uid and also containing a frothing agent w ich stabilizes the bubbles so that such coarse coal is gravitationally separated from the intermixed coarse shale by difierential settling of the shale in such 1i uid and separating such coarse coal from the iquid.

4. The rocess of separating coal from coarse and fine broken shale-bearing coal which consists in agitating a liquid containagent to entrain multitudes of bubbles and passing the broken shale-beararticles of intermediate sizes from uid, separating ing coal with said bubble-containing liquid through a jig so that the coarse coal is separate from the intermixed coarse shale 'by differential settling of the shale, and separatin the coarse coal from the liquid.

5. T e process of separating coal from coarse and fine broken shale-bearing coal of said coal and bubble-containing water t jig so that the coarse coal is separated rom the intermixed coarse shale by differential settling of the shale in the pulp, and se arating the purified coal from the top of tfie pulp partly by the gravity concentration and partlg by froth-flotation.

6, he process of coarse and fine shale-bearing coal the coarse coal bein too coarse to be fioate by bubble action, w ich consists in passing the broken shale-bearing coal through a liquid so that coarse shale is gravitationally separated from intermixed coarse coal by differential settling of the coarse'shale in such liquid, overflowing liquid carrying such coarse coal and fine solids in suspension, separating such coarse coal from the liquid and fine solids, agitating the separated liquid containing fine solids with a frothing agent to entrain multitudes of bubbles so that the light bubbles tend to offset the weight of suspended solids remaining in the liquid, passing further broken shale-bearing coal through the liquid containing the entrained bubbles to gravitationally separate intermixed coarse shale therefrom by differential settling of the shale, and separating further coal from the latter liquid.

7. The rocess of. separating coal from coarse an fine broken shale-bearing coal, the coarse coal being too coarse to be floated by bubble action, which consists in passing the broken shale-bearing coal through a liq-' uid so that such coarse coal is gravitationally sepfarate'd from intermixed coarse shale by di erential settling of the shale in such liqthe coal and liquid carrying unsettled shale from the settled shale, agitating the separated liquid carrying the unsettled'shale and the coal with a agent to entrain multitudes of bubbles in such liquid so that the light bubbles tend to ofi'set the weight of suspended solids remaining in the liquid to permit a further quantity of shale to settle therein, from the liquid and further settled shale the coal carried in the liquid.

8. The process of separating coal from coarse and fine broken shale-bearin coal, the coarse coal being too coarse to fie floated by bubble action, which consists in passing the broken shale-bearing coal through a liquid so that such coarse coal is avitationally separated from intermixe coarse separating coal from frothing and separating shale by difierential settling of shale, se arating the coal and liquid rom the sett ed shale agitatin the separated liquid carrying t e unsett ed shale and the coal with a frothing agent to entrain multitudes of bubbles in such liquid so that the light bubbles tend to offset the weight of suspended solids remaining in the liquid to permit a further quantity of shale to settle therein, such agitation also forming a coal-bearing froth, separating the coal-bearing frot from the liquid, and separately separting coarse coal from the liquld.

9. The process which consists in agitating impure coal in water in a series of gravity water concentrators, adding a fiocculating agent between two concentrators so that the water in a concentrator normally delivering finer coal also delivers fiocculated coal particles, separating the purified coal from its accom anying water, and returning the separate water to the first concentrator.

10. The rocess which consists in effecting "a partial coal in a jiglby separating part of the coal, conveying t e remaining coal in a pulp to a. second jig, agitating and adding a fiocculating agent intermediate the jigs, efiecting further concentration in the second ig, draining the accompanyin water from concentrated coal, and returning the separated water to the first jig 11. The process w ich consists in effecting a partial concentration of an impure coal in a jig by separating part of the coal, conveyin the remaining coalin a pulp to a secon jig through a centrifugal pump, addin air and a fiocculating agent during sai conveyance, efiectin further concentration in the second jig, raining the accompanying water from the concentrated coal, and returning the separated water to the first 12. he process of separating coal from broken coarse and fine shale-bearing coal,

concentration of an impure the coarse coal bein too coarse to be floated by bubble action, w ich consists in separating coarse shale from such coarse coal in liquid suspension in a jig, conveying to a second jig the solids and liquid separated from coarse shale, a itating and aerating the liquid containing t e solids in the second jig in the presence of a fiocculating agent to flocculate the particles of fine coal, and separatin substantially together such coarse coal and occulated fine coal from the liquid and other solids.

13. A coal concentrating apparatus comrising a jig, a'second jig, means for agitatmg coal and conveying it from the first jig to the second jig, and means for adding a fiocculating agent between the jigs so that the coal is agltated in its presence.

A coal concentrating apparatus comprismg a jig, a second jig, a centrifugal pump for agitating coal and conveying it from the first jig to the second jig, and means for adding air and a fiocculating agent between the jigs so that the coal is agitated with the air and agent by the pump.

A coal concentrating apparatus comprising a ig, a second jiigr, means for agitating and conveying coal om the first ji to the second jig, means for adding a occulating a ent between the jigs so that the coal is agitated with the agent, means for separating concentrated coal from the water, and means for returning the water to a jig.

16. A coal concetrating apparatus comprising a jig, a second jig, a centrifugal pum for agitating and conveying coal from the rst jig to t e second jig, means for adding air and a fiocculating agent so that the coal is agitated by the pump. with the air and agent, means for separating concentrated coal from the water, and means for returning the water to the first jig.

In testimony whereof I aflix my signature.

WARWICK STENNING. 

